The present invention relates to printing apparatus used, being connected to a host computer, and for example a dot impact serial printer.
FIG. 10 is a sectional view showing this type of printing apparatus in the prior art. Referring to the figure, a print head 1 performs spacing movement in a direction perpendicular to the page. A platen 2 is opposite to the print head 1. A continuous sheet, e.g., continuous form with preprinted frames, 3 is fed or conveyed, being wound over the platen 2. A tractor 4 having pins engaging perforations provided along edges of the continuous sheet 3 rotates to pull the continuous sheet 3 in the direction indicated by arrow 11 for forward feeding or line-feed, or in the reverse direction for rearward feeding or line-feed. A pinch roller 5 presses the continuous sheet 3 against the platen 2, rotation of which also pulls the continuous sheet 3 in the direction of arrow 11 or in the reverse direction. A pinch roller 8 presses a cut sheet, such as a slip with a preprinted frames, 6 against a drive roller 7, which thereby pulls the cut sheet 6 in the direction indicated by arrow 12 for forward feeding or line-feed, or in the reverse direction for rearward feeding or line-feed. Similarly, a pinch roller 10 presses the cut sheet 6 against a drive roller 9, which thereby pulls a cut sheet 6 in the direction indicated by arrow 12 or in the reverse direction.
Thus, the printing apparatus shown in FIG. 10 is provided with a first conveyance system C1 which comprises a continuous sheet conveyance mechanism M1 comprising the platen 2, the tractor 4 and the pinch roller 5 for conveying the continuous sheet 3 along a first conveyance path, and a drive system, not shown, comprising a drive motor, etc. for driving the continuous sheet conveyance mechanism M1, and a second conveyance system C2 which comprises a cut sheet conveyance mechanism M2 comprising the drive rollers 7 and 9, and the pinch rollers 8 and 10 for conveying the cut sheet 6 along a second conveyance path, and a second drive system, not shown, comprising a drive motor, etc. for driving the cut sheet conveyance mechanism M2.
Next, the continuous sheet conveyance operation and cut sheet conveyance operation of the printing apparatus of the type described above is described. FIG. 11 shows the state in which a continuous sheet 3 is conveyed. The continuous sheet 3 is conveyed forward in the direction indicated by arrow 11 by the rotational driving of the platen 2 and the tractor 4. It is essential that the platen 2 is formed of a material which can withstand the impact of the print head 1 and which has a coefficient of friction suitable for conveying the printing sheet. Hard rubber or the like is generally used as the material for the platen 2. FIG. 12 shows the state in which a cut sheet 6 is conveyed. The cut sheet 6 is driven forward in the direction indicated by arrow 12 by the rotational driving of the drive rollers 7 and 9 and the pinch rollers 8 and 10. During the cut sheet conveyance, the continuous sheet conveyance mechanism M1 is not moving.
As described above, in a printing apparatus having a continuous sheet conveyance mechanism M1 and a cut sheet conveyance mechanism M2, which can be driven independently, the printing and conveyance of a cut sheet can be conducted in the state in which the continuous sheet 3 is mounted on the platen 2 and the tractor 4. The continuous sheet conveyance mechanism M1 including the platen 2 is not moving.
Since the printing apparatus of the type described is configured as described above, and the platen 2 is not moving when the cut sheet is printed and conveyed, the print head 1 strikes the same parts of the platen 2 repetitively. As a result, wear, and impression (indentation as a result of impact by the print head) are formed on the platen 2, which leads to degradation in the performance of the printing sheet conveyance, degradation in the printing quality, and consequent shortening of the life of the printing apparatus.